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Fix return type of visit() to properly take cv& into account

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This commit is contained in:
Peter Dimov
2017-06-01 19:24:50 +03:00
parent c891c8e205
commit 77e8c46074
2 changed files with 63 additions and 18 deletions
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55
include/boost/variant2/variant.hpp
View File

@@ -81,22 +81,22 @@ template<std::size_t I, class T> using variant_alternative_t = typename variant_
namespace detail
{
template<class I, class T, class Q> using var_alt_t = mp_invoke<Q, variant_alternative_t<I::value, T>>;
template<class I, class T, class Q> using var_alt_impl = mp_invoke<Q, variant_alternative_t<I::value, T>>;
} // namespace detail
template<std::size_t I, class T> struct variant_alternative
{
};
template<std::size_t I, class T> struct variant_alternative<I, T const>: mp_defer< variant2::detail::var_alt_t, mp_size_t<I>, T, mp_quote<std::add_const_t>>
template<std::size_t I, class T> struct variant_alternative<I, T const>: mp_defer< variant2::detail::var_alt_impl, mp_size_t<I>, T, mp_quote<std::add_const_t>>
{
};
template<std::size_t I, class T> struct variant_alternative<I, T volatile>: mp_defer< variant2::detail::var_alt_t, mp_size_t<I>, T, mp_quote<std::add_volatile_t>>
template<std::size_t I, class T> struct variant_alternative<I, T volatile>: mp_defer< variant2::detail::var_alt_impl, mp_size_t<I>, T, mp_quote<std::add_volatile_t>>
{
};
template<std::size_t I, class T> struct variant_alternative<I, T const volatile>: mp_defer< variant2::detail::var_alt_t, mp_size_t<I>, T, mp_quote<std::add_cv_t>>
template<std::size_t I, class T> struct variant_alternative<I, T const volatile>: mp_defer< variant2::detail::var_alt_impl, mp_size_t<I>, T, mp_quote<std::add_cv_t>>
{
};
@@ -1065,16 +1065,9 @@ template<class... T> constexpr bool operator>=( variant<T...> const & v, variant
}
// visitation
template<class F> constexpr auto visit( F&& f ) -> decltype(std::forward<F>(f)())
{
return std::forward<F>(f)();
}
namespace detail
{
template<class T> using remove_cv_ref = std::remove_cv_t<std::remove_reference_t<T>>;
template<class F> struct Qret
{
template<class... T> using fn = decltype( std::declval<F>()( std::declval<T>()... ) );
@@ -1082,13 +1075,41 @@ template<class F> struct Qret
template<class L> using front_if_same = mp_if<mp_apply<mp_same, L>, mp_front<L>>;
template<class F, class... V> using Vret = front_if_same<mp_product_q<Qret<F>, remove_cv_ref<V>...>>;
template<class V> using var_size = variant_size<std::remove_reference_t<V>>;
template<class V, class N, class T = variant_alternative_t<N::value, std::remove_reference_t<V>>> using apply_cv_ref_ = mp_if<std::is_reference<V>, T&, T>;
#if BOOST_WORKAROUND( BOOST_MSVC, <= 1910 )
template<class V> struct apply_cv_ref_impl
{
template<class T> using _f = apply_cv_ref_<V, T>;
using L = mp_iota<var_size<V>>;
using type = mp_transform<_f, L>;
};
template<class V> using apply_cv_ref = typename apply_cv_ref_impl<V>::type;
#else
template<class V> using apply_cv_ref = mp_transform_q<mp_bind_front<apply_cv_ref_, V>, mp_iota<var_size<V>>>;
#endif
template<class F, class... V> using Vret = front_if_same<mp_product_q<Qret<F>, apply_cv_ref<V>...>>;
} // namespace detail
template<class F> constexpr auto visit( F&& f ) -> decltype(std::forward<F>(f)())
{
return std::forward<F>(f)();
}
template<class F, class V1> constexpr auto visit( F&& f, V1&& v1 ) -> variant2::detail::Vret<F, V1>
{
return mp_for_index<mp_size<variant2::detail::remove_cv_ref<V1>>>( v1.index(), [&]( auto I ){
return mp_for_index<variant2::detail::var_size<V1>>( v1.index(), [&]( auto I ){
return std::forward<F>(f)( get<I>( std::forward<V1>(v1) ) );
@@ -1099,7 +1120,7 @@ template<class F, class V1> constexpr auto visit( F&& f, V1&& v1 ) -> variant2::
template<class F, class V1, class V2> constexpr auto visit( F&& f, V1&& v1, V2&& v2 ) -> variant2::detail::Vret<F, V1, V2>
{
return mp_for_index<mp_size<variant2::detail::remove_cv_ref<V1>>>( v1.index(), [&]( auto I ){
return mp_for_index<variant2::detail::var_size<V1>>( v1.index(), [&]( auto I ){
auto f2 = [&]( auto&&... a ){ return std::forward<F>(f)( get<I.value>( std::forward<V1>(v1) ), std::forward<decltype(a)>(a)... ); };
return visit( f2, std::forward<V2>(v2) );
@@ -1109,7 +1130,7 @@ template<class F, class V1, class V2> constexpr auto visit( F&& f, V1&& v1, V2&&
template<class F, class V1, class V2, class V3> constexpr auto visit( F&& f, V1&& v1, V2&& v2, V3&& v3 ) -> variant2::detail::Vret<F, V1, V2, V3>
{
return mp_for_index<mp_size<variant2::detail::remove_cv_ref<V1>>>( v1.index(), [&]( auto I ){
return mp_for_index<variant2::detail::var_size<V1>>( v1.index(), [&]( auto I ){
auto f2 = [&]( auto&&... a ){ return std::forward<F>(f)( get<I.value>( std::forward<V1>(v1) ), std::forward<decltype(a)>(a)... ); };
return visit( f2, std::forward<V2>(v2), std::forward<V3>(v3) );
@@ -1119,7 +1140,7 @@ template<class F, class V1, class V2, class V3> constexpr auto visit( F&& f, V1&
template<class F, class V1, class V2, class V3, class V4> constexpr auto visit( F&& f, V1&& v1, V2&& v2, V3&& v3, V4&& v4 ) -> variant2::detail::Vret<F, V1, V2, V3, V4>
{
return mp_for_index<mp_size<variant2::detail::remove_cv_ref<V1>>>( v1.index(), [&]( auto I ){
return mp_for_index<variant2::detail::var_size<V1>>( v1.index(), [&]( auto I ){
auto f2 = [&]( auto&&... a ){ return std::forward<F>(f)( get<I.value>( std::forward<V1>(v1) ), std::forward<decltype(a)>(a)... ); };
return visit( f2, std::forward<V2>(v2), std::forward<V3>(v3), std::forward<V4>(v4) );
@@ -1131,7 +1152,7 @@ template<class F, class V1, class V2, class V3, class V4> constexpr auto visit(
template<class F, class V1, class V2, class... V> constexpr auto visit( F&& f, V1&& v1, V2&& v2, V&&... v ) -> variant2::detail::Vret<F, V1, V2, V...>
{
return mp_for_index<mp_size<variant2::detail::remove_cv_ref<V1>>>( v1.index(), [&]( auto I ){
return mp_for_index<variant2::detail::var_size<V1>>( v1.index(), [&]( auto I ){
auto f2 = [&]( auto&&... a ){ return std::forward<F>(f)( get<I.value>( std::forward<V1>(v1) ), std::forward<decltype(a)>(a)... ); };
return visit( f2, std::forward<V2>(v2), std::forward<V>(v)... );

26
test/variant_visit.cpp
View File

@@ -7,6 +7,7 @@
// http://www.boost.org/LICENSE_1_0.txt
#include <boost/variant2/variant.hpp>
#include <boost/mp11.hpp>
#include <boost/core/lightweight_test.hpp>
#include <boost/core/lightweight_test_trait.hpp>
#include <type_traits>
@@ -15,6 +16,19 @@
#include <cstdio>
using namespace boost::variant2;
using boost::mp11::mp_size_t;
struct X
{
};
struct F
{
mp_size_t<1> operator()( X& ) const;
mp_size_t<2> operator()( X const& ) const;
mp_size_t<3> operator()( X&& ) const;
mp_size_t<4> operator()( X const&& ) const;
};
int main()
{
@@ -84,7 +98,17 @@ int main()
BOOST_TEST_EQ( (visit( []( auto x1, auto x2, auto x3, auto x4 ){ return (long long)(x1 * 100) * 100000000 + (long long)(x2 * 100) * 100000 + (long long)(x3 * 10000) + (int)x4; }, v1, v2, v3, v4 )), 10031462800 + 'A' );
visit( []( auto x1, auto x2, auto x3, auto x4 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); BOOST_TEST_EQ( x3, 6.28 ); BOOST_TEST_EQ( x4, 'A' ); }, v1, v2, v3, v4 );
visit( []( auto x1, auto x2, auto x3, auto x4 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); BOOST_TEST_EQ( x3, 6.28 ); BOOST_TEST_EQ( x4, 'A' ); }, std::move(v1), std::move(v2), std::move(v3), std::move(v4) );
visit( []( auto x1, auto x2, auto x3, auto x4 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); BOOST_TEST_EQ( x3, 6.28 ); BOOST_TEST_EQ( x4, 'A' ); }, std::move(v1), std::move(v2), std::move(v3), std::move(v4) );
}
{
variant<X> v;
variant<X> const cv;
BOOST_TEST_EQ( decltype(visit(F{}, v))::value, 1 );
BOOST_TEST_EQ( decltype(visit(F{}, cv))::value, 2 );
BOOST_TEST_EQ( decltype(visit(F{}, std::move(v)))::value, 3 );
BOOST_TEST_EQ( decltype(visit(F{}, std::move(cv)))::value, 4 );
}
return boost::report_errors();